The present invention is related to a grinder, and more particularly to a pneumatic grinder in which the grinding disc can be easily changed.
A pneumatic grinder has a grinding disc mounted on the bottom of the grinder for grinding a work piece. The grinding disc is screwed with a rotary shaft of the grinder by a thread rod located on a top surface of the grinding disc. The rotary shaft is eccentrically pivotally connected with and is driven by a drive shaft of the pneumatic grinder. In operation, it is necessary to frequently replace the grinding disc.
Conventionally, when replacing the grinding disc, a flat wrench is extended into the bottom of the grinder for clogging the rotary shaft of the grinder. Under such circumstance, the grinding disc can be unscrewed from the rotary shaft and taken off. Similarly, when installing the grinding disc, it is also necessary to fix the rotary shaft. However, it is impossible for a user to directly see the state of the wrench fitted on the rotary shaft. Therefore, such replacement operation is quite inconvenient and time-consuming as well as dangerous.
European Patent No. 235,598 discloses an electric grinding tool that has lock for one section of a drive shaft secured against rotation by a lock member (a spring-loaded bolt).
Similarly, U.S. Pat. Nos. 4,400,995, 3,899,852, 3,872,951, 2,211,216, and 1,270,808 all disclose power rotary tools in which lock members lock drive shafts against rotation.
U.S. Pat. No. 5,766,062 discloses a power tool in which a lock member (an arresting device) locks a balancing device that is connected and coaxial with a drive shaft (spindle) for stopping the drive shaft from rotating.
All of the lock members of the above-mentioned patents directly stop the drive shafts of the tools from rotating. It is easy to chuck the drive shaft for its axial is stationary. For a pneumatic grinder, it is easy to chuck the drive shaft too, while it is uneasy to chuck the rotary shaft for its axial is not stationary. And for a pneumatic grinder, stopping the drive shaft is useless for changing a grinding disc, since the rotary shaft still rotates.
It is therefore tried by the inventor to develop a pneumatic grinder for solving the above problem existing in the conventional grinder.